What's with the NorCal Doublet?
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- čas přidán 20. 01. 2023
- In this video we take a look at an easy to build, popular dipole-style tunable antenna: The NorCal Doublet. See build instructions here: www.norcalqrp.org/norcaldoubl...
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Great vid! Doublets are fantastic antennas. the open wire has low loss thru the feedline even with poor vswr (vs coax), so actually very efficient as a multiband antenna. the 44’ size has dipole-pattern propagation at all bands 10-40, so can be oriented for predictable directivity, which is great here on the coast. one thing to watch for is that you can get losses with open wire in proximity to ground or metallic objects that “unbalance” the balanced line. I’ve seen some folks use a short coax run to a balun to get clear of the house/ground, which is a pretty good tradeoff vs making a weird open-wire pass-thru in a wall or window-frame, as long as the coax is kept as short as possible.
That's an interesting note about metallic objects unbalancing it. One thing I did observe later in the activation: I went to try to chase s2s on 20m and could only get a 3:1 match on that band. Odd bc it had tuned 1:1 earlier in the day. Now I wonder if my cell phone or something else was too close to the feedline then. The other bands still tuned 1:1 fine though 🤷🏼
@@N7KOM🤷♂️ sounds reasonable. iirc the rule of thumb is to keep possible couplings > than 2x the inter-wire spacing for open wire. I usually try to move my position to keep it off the ground , but I grabbed myself a 3’ coax bnc jumper and a bnc:bnc connector to try with my 1:1 k6ark balun, gonna give it a try with my norcal next time out. if nothing else it gets me 3’ higher up 😂
Cheers for the authentic wire stripping moment 😅 2:29
I gotta try that antenna! Thanks for sharing!
Let us know how it goes!
I really love these simple antennas. I built a speaker wire doublet and it tunes on the kx2 on many of the bands. I like the computer wires slim profile though. Awesome stuff Tim!
Thank you. Yes, I can't wait to try it out as a base station antenna and run the computer cable under a shut window. 73!
I haven’t built one with ribbon cable, but I built one with 16ga THHN that I had in the garage. I also built open feed line with the same wire.
It’s a little bulky, but is regularly deployed with the feedline to a 4:1 balun and a short coax run to the rig. It’s a solid antenna if you need to be frequency agile.
Cebick thought highly of it. That’s s good recommendation.
Doublets are great, though sometimes a bit tricky to set up on summit. I built a speaker-wire doublet for my first SOTA antenna, but haven't pulled it out in quite a while.
I think I'll still stick with the EFRW for portable use.
Neat idea. I've done speaker wire before, but the slim profile looks cool. Also, if I'd thought Cooper Mountain was a SOTA I'd have spent more time there before I moved out highway 30. I walked it a couple times from the old house.
Love the build, and it is well within my limited skill set. Now, I have to track down some old computer wire! 73!
The hardest part was finding time to take it up to a summit to test! 73!
Wow great project congratulations is work.73 from kb2uew
Thanks a lot!
It looks like the easiest source for suitable wire is four-conductor ribbon intended for RGB LED installs. You can get 100' (probably 30m/98.5') on Amazon for $20, which is markedly cheaper than proper IDC ribbon cable. There's even one listing that comes with four little pieces of heatshrink for $17, which might shrink small enough to replace the fold-back ziptie. I'd probably keep some zipties in the bag just in case that failed, though.
(I think this is the first time I've had a visceral "Thanks, I hate it" reaction to an antenna design 😅)
Are you saying I should make an led antenna? 🥳🤯
The ultimate gamers HF antenna 😆
@@N7KOM Y'know, I have no idea what happens if you put diodes in a feedline. I imagine the capacitance is a a nightmare, as reverse-biased LEDs are a classic QRPp varicap.
I thought you might be amused: I pulled out some 15 year old ladder line (from making 2m j-poles for weather balloon stuff), and put together a doublet. It's incredibly poorly mounted, but working well enough, and is a great demonstration of "A compromise antenna is better than no antenna." My other antenna at home is an early Alpha loop, which does okay-ish on 15m to 30m, but is receive-only outside that range.
OTOH, this doublet, installed as a janky sloper from 12' high, is pulling in tons of stuff, and gets out well enough for FT-8 on 10 to 20. Waiting for night to try 30, 40, and 80, but I could get all of them to decent SWRs with an MFJ-941E, so 🤞that it's actually matched and not just a very complicated resistor.
I'm really hoping 80m works out, as there's a local slow CW net out of Berkeley that I've wanted to join in on for practice for years now, but didn't have an antenna for.
It'll take a few days to determine whether I should be thanking or blaming you for this one. Until then, a tentative thank you for getting me to try this out!
73 de AJ9BM
@@joshmyer9 That's awesome. Let me know how it goes! 40m has been pretty good anytime of day lately. I still need to try getting on 80 meters sometime.
This is a slick build. Looks like a winner. -73 KK7DAK
Thank you!
Hey Tim, nice job on the build and field test video! I need to find an easy local SOTA summit to use for antenna testing etc. I'll definitely give one of those doublets a try. My go-to SOTA antenna of late has been a 20-meter end fed half wave which I connect via a tiny Unun; the entire thing weighs about 4 ounces. I pretty much only work 2 and 20 meters during SOTA, but it would be great to have a multi-band option. Keep up the good work with the videos and hopefully we'll be able to pull off a S2S one of these days. 73s! Mark K0EHR
Hey Mark, great to hear from you. I recall that you were using an off-center dipole for your SOTA activations. Cool that you've given the EFHW a go. I need to build a new one of those. You should definitely look at getting a multi-band antenna, or at least a higher-band antenna going. I've had some really cool QSOs on 10 and 15 meters lately. Very fun bands to get on to and neat to get some new countries in the logbook. You use a IC-705, right? 73 de Tim N7KOM
@@N7KOM Hey Tim, you are correct--I'm still using the IC-705. I am always looking at the tradeoffs between having to carry my LDG tuner and being able to use multiple bands, vs going with the EFHW. It's really only about 1/2 pound difference, and you have a great point around the advantages of the multi-band approach, particularly of late with cycle 25 finally kicking in. I may go back to my OCFD as it performs really well and weighs next to nothing. I also like your Norcal Doublet--maybe I'll make one of those my next QRP project!
73s, Mark K0EHR
@@markehr My next project is making some traps for yet-another- end fed half wave. You could always try that, or links for a multi-bander without a tuner.
OR, from K6ARK's EFHW kit: "Adding a small loading coil can help bring 20 m, 15 m, and 10 m into resonance on a 40m wire. Start by attaching a spool of antenna wire to the matching unit. Use the ¾” long piece of .7” dia tubing to wrap about 12 turns of wire, 6 feet from the feed point of the antenna. Keep it from uncoiling with tape or slits in the plastic. Unfurl enough wire for resonance on 40m, then test on 20m and 15m. Adjust the coil as necessary to bring those bands into resonance. Once the right location and turns are found, secure the coil with heat shrink, cut the wire long, and trim to resonance." I haven't tried this myself yet, but seems like a great solution to add those higher bands.
Can you make an antenna out of a couple of 3.5 floppy drives?
a single 3.5 floppy is a 1/22 wave on 2 meters!
What is the gauge of the ribbon wire used?
28 gauge on this one. Pretty thin and fragile!
No 1:4 balun?
Not needed! The spacing of the computer cable wires acts similar to a ladder line. The tuner takes care of the rest.
The piano music in the background is REALLY distracting!